1. Field of the Invention
The present invention relates to an automated optical inspection system and, more particularly, to an automated optical inspection system employing a combination of reflective and thru-lighting means for detecting defects in work pieces having one or more apertures, such as printed circuit boards or cathode ray tube shadow masks.
2. Prior Art
There are many optical inspection systems available in the prior art. Illumination configurations for inspection are typically applied in either of two configurations. A reflective illumination configuration provides for inspection of surface features and planes, while a "backlight" or "thru-light" configuration provides for inspection of holes in a mask or printed circuit board such as drilled or etched holes that go entirely through the product being inspected.
The following patents illustrate the prior art optical inspection systems:
U.S. Pat. No. 5,185,638 teaches a flexible and automated optical inspection system for printed circuit boards with illumination of surface features and multiple light sources to include the collection of light reflected from the surface.
The patent does not teach nor suggest an automated optical inspection system which provides simultaneous inspection of surface defects and drilled or etched holes in a product being inspected as it taught and claimed herein.
U.S. Pat. No. 5,197,105 teaches a method of reading an optical image of an inspected surface which employs multiple wavelength energy sources with multiple energy detection sensors specifically related to angular aperture applications.
The patent does not teach nor suggest an automated optical inspection system which provides simultaneous inspection of surface defects and drilled or etched holes in a product being inspected as it taught and claimed herein.
U.S. Pat. No. 5,216,479 discloses an optical inspection system with the imaging of an aperture in a reflecting surface and a first focal line co-planar with a first surface of a laminate. The patent teaches a single side only reflective optical inspection system.
The patent does not teach nor suggest an automated optical inspection system which provides simultaneous inspection of surface defects and drilled or etched holes in a product being inspected as it taught and claimed herein.
U.S. Pat. No. 5,268,735 teaches an optical inspection apparatus which can observe a light transmitted portion and a light reflected portion within objects of inspection distinguishable from each other within the same field of vision.
The patent does not teach nor suggest an automated optical inspection system which provides simultaneous inspection of surface defects and drilled or etched holes in a product being inspected as it taught and claimed herein.
U.S. Pat. No. 5,288,991 teaches an optical inspection system in which the surface of a substrate is scanned by a linear charge coupled device (CCD). The surface is illuminated in a narrowly focused strip from a broad band light source that is selectively wavelength filtered to optimize image contrast to the applicable characteristics of the surface under inspection.
The patent does not teach nor suggest an automated optical inspection system which provides simultaneous inspection of surface defects and drilled or etched holes in a product being inspected as it taught and claimed herein.
U.S. Pat. No. 5,301,012 teaches an optical technique for rapid inspection of via holes under etch and decontamination. The sensitivity and resolution of the automatic inspection system is enhanced by fully illuminating an area corresponding to a nominal-feature-shaped shape formed on a surface. Scanning of the illuminated area provides resolution of defects far smaller than the area of the illuminated spot. The patent employs a laser light source which provides for inspecting one surface of the product to be inspected.
The patent does not teach nor suggest an automated optical inspection system which provides simultaneous inspection of surface defects and drilled or etched holes in a product being inspected as it taught and claimed herein.
Although the prior art generally teaches optical inspection systems, the prior art does not teach an automated optical inspection system which allows for simultaneous reflective and thru-inspection of drilled or etched holes in a product being inspected.